/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.graph.drivers.parameter;

import org.apache.flink.api.java.utils.ParameterTool;
import org.apache.flink.graph.drivers.parameter.IterationConvergence.Value;

/**
 * Iterative algorithms which converge can be terminated with a maximum number
 * of iterations or a convergence threshold which stops computation when the
 * total change in scores is below a given delta.
 *
 * <p>If the command-line configuration specifies neither a number of iterations
 * nor a convergence threshold then a default number of iterations is used
 * with an infinite convergence threshold. Otherwise, when either value is
 * configured then an unset value is set to infinity.
 */
public class IterationConvergence
implements Parameter<Value> {

	private final int defaultIterations;

	private final Value value = new Value();

	/**
	 * Add this parameter to the list of parameters stored by owner.
	 *
	 * @param owner the {@link Parameterized} using this {@link Parameter}
	 * @param defaultIterations the default number of iterations if neither
	 *                          the number of iterations nor the convergence
	 *                          threshold are specified
	 */
	public IterationConvergence(ParameterizedBase owner, int defaultIterations) {
		owner.addParameter(this);
		this.defaultIterations = defaultIterations;
	}

	@Override
	public String getUsage() {
		return "[--iterations ITERATIONS] [--convergence_threshold CONVERGENCE_THRESHOLD] ";
	}

	@Override
	public boolean isHidden() {
		return false;
	}

	@Override
	public void configure(ParameterTool parameterTool) {
		if (!parameterTool.has("iterations") && !parameterTool.has("convergence_threshold")) {
			// no configuration so use default iterations and maximum threshold
			value.iterations = defaultIterations;
			value.convergenceThreshold = Double.MAX_VALUE;
		} else {
			// use configured values and maximum default for unset values
			value.iterations = parameterTool.getInt("iterations", Integer.MAX_VALUE);
			Util.checkParameter(value.iterations > 0,
				"iterations must be greater than zero");

			value.convergenceThreshold = parameterTool.getDouble("convergence_threshold", Double.MAX_VALUE);
			Util.checkParameter(value.convergenceThreshold > 0,
				"convergence threshold must be greater than zero");
		}
	}

	@Override
	public Value getValue() {
		return value;
	}

	/**
	 * Encapsulate the number of iterations and the convergence threshold.
	 */
	public static class Value {
		public int iterations;
		public double convergenceThreshold;
	}
}
